This application claims priority to U.S. Provisional Patent No. 61/191,359, filed on Sep. 8, 2008. The provisional application is hereby fully incorporated by reference.
The present disclosure relates to wind turbines, particularly systems and/or methods for protecting wind turbines in high wind conditions.
Conventional wind turbines used for power generation generally have two to five open blades arranged like a propeller, the blades being mounted to a horizontal shaft attached to a gear box which drives a power generator. Such turbines are generally known as horizontal axis wind turbines, or HAWTs. Although HAWTs have achieved widespread usage, their efficiency is not optimized. In particular, they will not exceed the Betz limit of 59.3% efficiency in capturing the potential energy of the wind passing through it.
Conventional wind turbines have three blades and are oriented or pointed into the wind by computer controlled motors. These turbines typically require a supporting tower ranging from 60 to 90 meters in height. The blades generally rotate at a rotational speed of about 10 to 22 rpm. A gear box is commonly used to step up the speed to drive the generator, although some designs may directly drive an annular electric generator. Some turbines operate at a constant speed. However, more energy can be collected by using a variable speed turbine and a solid state power converter to interface the turbine with the generator.
When conventional HAWTs are exposed to excessively high speed winds, the additional wind energy can produce enough power to burn out the generator of otherwise damage the turbine. In such strong wind conditions, the blades can be furled or the entire driveshaft can be yawed to cause a severe reduction in the rotor power coefficient. These methods work well for protecting the turbine at wind speeds of 45-50 miles per hour. However, in hurricane force winds of 74 mph or higher, damage may still occur.
In addition, because the blades of a HAWT are located so close to the tower, strong winds are known to bend the blades back so that the blades hit the tower. This is phenomenon is known as a tower strike. If guy wires are used to stabilize the tower, they generally must be attached to the tower at a point below the lowest reach of the blades to avoid being struck by the blades. Because the blades of conventional HAWTs are located so close to the azimuthal (yaw) pivot point, the tower supporting the turbine generally cannot be a tripod type tower with a wide base. In addition, the HAWT cannot generally be mounted on a wide structure, such as a building.
It would be desirable to provide different methods by which a wind turbine can be protected from excessive wind speeds.